Tunable optical structures

ABSTRACT

Aspects of the present disclosure describe optical structures and devices, and more particularly to improved, tunable optical structures including optical gratings that are dynamically affected and/or tuned by acousto-optic or electro-optic mechanisms.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/558,920 filed Sep. 15, 2017 the entire contentsof which are incorporated by reference as if set forth at length herein.

TECHNICAL FIELD

This disclosure relates generally to optical structures and devices, andmore particularly to improved, tunable optical structures includingoptical gratings that are dynamically affected and/or tuned byacousto-optic or electro-optic mechanisms.

BACKGROUND

As is known, systems, methods, and structures that employ photonicintegrated circuits (PICs) and directed light emitted therefrom areexpected to find widespread applicability in many contemporaryapplications including light detection and ranging (LiDAR), free spacecommunications, and holographic displays. Accordingly, systems, methods,and structures that facilitate the emission or directional control oflight emitted from PICs would represent a welcome addition to the art.

SUMMARY

An advance in the art is made according to aspects of the presentdisclosure directed to dynamically tunable optical structures includingoptical gratings that are induced in the structures by the applicationof acousto-optic and/or electro-optic mechanisms.

In sharp contrast to the prior art, optical structures according to thepresent disclosure advantageously provide an out-of-plane emission oflight relative to the optical structure in addition to exhibitingdynamic tunability.

BRIEF DESCRIPTION OF THE DRAWING

A more complete understanding of the present disclosure may be realizedby reference to the accompanying drawing in which:

FIG. 1 is a schematic illustrating a prior-art edge coupledacousto-optic deflector;

FIG. 2 is a schematic illustrating a perturbation grating inducing aguided optical mode to be emitted out of plane for a waveguide accordingto aspects of the present disclosure;

FIG. 3 is a schematic illustrating out of plane emission induced by asurface acoustic wave (SAW) according to aspects of the presentdisclosure;

FIG. 4 is a schematic illustrating the generation of a standing acousticwave by reflection from a boundary to while eliminating Doppler shiftingof emitted light according to aspects of the present disclosure;

FIG. 5 is a schematic illustrating the generation of a standing acousticwave from two opposed acoustic transducers to eliminate Doppler shiftingof emitted light according to aspects of the present disclosure;

FIG. 6 is a schematic illustrating the generation of surface acousticwaves in both longitudinal and lateral directions through the effect oftwo acoustic transducers and the resulting directing of light out ofplane in two dimensions according to aspects of the present disclosure;

FIG. 7 is a schematic illustrating a tree structure including phaseshifters that steers light in a lateral direction while a SAW steers thelight in a longitudinal direction according to aspects of the presentdisclosure;

FIG. 8 is a schematic illustrating an optical phased array arrangementincluding individual acoustic transducer actuators according to aspectsof the present disclosure;

FIG. 9 is a schematic illustrating an optical phased array arrangementincluding individual acoustic transducers that advantageously eliminatephase shifters according to aspects of the present disclosure;

FIG. 10 is a schematic illustrating an optical phased array includingacoustic transducers configured such that controlling the phase(s) ofacoustic waves effect control of the phased array emission(s) accordingto aspects of the present disclosure;

FIG. 11 is a schematic illustrating how acoustic mode may be induced andguided in a photonics waveguide according to aspects of the presentdisclosure;

FIG. 12 is a schematic illustrating piezoelectric material deposited ona silicon waveguide and inducing a vertical sheer mode according toaspects of the present disclosure;

FIG. 13 is a schematic illustrating piezoelectric material positionedadjacent to a side of an optical waveguide to induce a sideways acousticmode according to aspects of the present disclosure;

FIG. 14 is a schematic illustrating piezoelectric material positioned atan end of an optical waveguide to induce a compressive wave along alength of the waveguide according to aspects of the present disclosure;

FIG. 15 is a schematic illustrating interdigitated piezoelectricmaterial positioned adjacent to a side of an optical waveguide to inducecompressive acoustic waves along a length of the waveguide according toaspects of the present disclosure;

FIG. 16 is a schematic illustrating a periodic series of doped regionsof an optical waveguide configured to convert RF electronic energy intoan acoustic wave from internal Coulomb force(s) according to aspects ofthe present disclosure;

FIG. 17 is a schematic illustrating electrooptic tuning of an opticalgrating by changing an effective index of the grating a phase matchingcondition and direction of emission changes as well according to aspectsof the present disclosure;

FIG. 18 is a schematic illustrating an application of a voltage across ap-n junction of an optical waveguide changes free carrier density in thewaveguide such that direction of emission is changed according toaspects of the present disclosure;

FIG. 19 is a schematic illustrating a voltage controlled p-n junctionoperating as a tunable grating according to aspects of the presentdisclosure;

FIG. 20 is a schematic illustrating the application of a periodicvoltage function to p-n junction segments of a waveguide resulting inthe perturbation of a refractive index of the waveguide according toaspects of the present disclosure;

FIG. 21 is a schematic illustrating the application of a standing RFwave to p-n junction segments of a waveguide resulting in the formationof a grating having a period that is tuned according to the frequency ofthe RF signal according to aspects of the present disclosure;

FIG. 22 is a schematic illustrating the application of a voltage to asemiconductor-on-semiconductor capacitor results in charge build-upaccording to aspects of the present disclosure;

FIG. 23 is a schematic illustrating the creation of a periodic indexperturbation in a silicon waveguide from the application of a periodicpattern of voltages to polysilicon segments of the waveguide accordingto aspects of the present disclosure;

FIG. 24 is a schematic illustrating short and thin segments ofpolysilicon deposited above a silicon waveguide that are controlled byindividual voltages according to aspects of the present disclosure;

FIG. 25 is a schematic illustrating long segments of polysilicon used toexcite a plurality of waveguides in parallel according to aspects of thepresent disclosure;

FIG. 26 is a schematic illustrating generation of a periodic voltagepattern in an optical waveguide from a standing RF according to aspectsof the present disclosure;

The illustrative embodiments are described more fully by the Figures anddetailed description. Embodiments according to this disclosure may,however, be embodied in various forms and are not limited to specific orillustrative embodiments described in the drawing and detaileddescription.

DESCRIPTION

The following merely illustrates the principles of the disclosure. Itwill thus be appreciated that those skilled in the art will be able todevise various arrangements which, although not explicitly described orshown herein, embody the principles of the disclosure and are includedwithin its spirit and scope.

Furthermore, all examples and conditional language recited herein areintended to be only for pedagogical purposes to aid the reader inunderstanding the principles of the disclosure and the conceptscontributed by the inventor(s) to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat any block diagrams herein represent conceptual views ofillustrative circuitry embodying the principles of the disclosure.

Unless otherwise explicitly specified herein, the FIGs comprising thedrawing are not drawn to scale.

Acoustic Tuning

By way of some further background we turn our attention to FIG. 1 whichshows a schematic illustrating a prior art, edge coupled acousto-opticdeflector (AOD). As is known in the art, such an AOD employs anacousto-optic effect to deflect light using sound waves. As illustratedin FIG. 1, an acoustic transducer—positioned at one end of an opticalmaterial—generates acoustic waves which generally propagate along asurface of the material as a surface acoustic wave (SAW).Advantageously, the generation of acoustic waves may be accomplished viaknown piezoelectric materials.

While not specifically shown in the figure, a wave vector of theacoustic wave—which generally depends on a period of any interdigitatedpiezoelectric transducer and frequency of microwave excitation) is addedto the propagation vector of an incoming light beam as it passes throughthe material such that one or more deflected beams may result. As aresult, the energy of the light beam is depleted of energy andintensity(ies) of through beam(s) is/are reduced. If only one deflectedbeam is desired, the wavelength of the SAW must be small so short periodtransducers and high frequency RF excitation is generally required.

We note at this point that the device shown in FIG. 1 may deflect(steer) light in a single, in-plane dimension only. And while suchstructures and systems constructed therefrom may be suitable for certainfree-space input and output configurations, their application tophotonic integrated circuits are at least more challenging.

In sharp contrast to any deflection achieved by edge coupledacousto-optic deflectors such as those illustrated in FIG. 1, structuresaccording to the present disclosure which we shall illustratively showand describe, advantageously emit light out of the plane of the opticalmaterial (i.e., optical waveguide). Operationally, such out-of-planeemission is affected by inducing a change in refractive index in andaround an optical waveguide due to strain or stress caused by anacoustic wave.

Turning now to FIG. 2, there is shown a schematic illustration of aperturbation grating and its effect on a guided light beamtraversing—for example—a silicon waveguide. Depicted illustratively inthat figure are three gratings namely, a long period grating, a matchedperiod grating, and a short period grating. As may be observed from thatfigure, the guided light is emitted out of the waveguide because of theperturbations around the waveguide and the direction of the emission(s)is/are determined by the period of the perturbations. Generally, when aBragg condition is met, light is emitted in a direction substantiallyperpendicular to its direction of travel. Shorter periods will cause abackward directed emission (reverse direction to the direction of lighttravel) while a longer period grating will cause a forward directedemission (in the direction of travel of the light). Note that in thisillustrative FIG. 2—and as generally known in the art—the perturbations(gratings) are fixed, and therefore to change the direction of emissionone must either physically the index of the waveguide or change thewavelength of the light.

Advantageously, systems, methods, and structures according to thepresent disclosure are not so infirmed.

FIG. 3 is a schematic, cross-sectional view illustrating out-of-planeemission induced by a surface acoustic wave according to aspects of thepresent disclosure. As may be observed from that figure, an opticalwaveguide structure includes an optical guiding layer throughout itslength, the waveguide structure including an acoustic transducer.

Operationally, the transducer will generate a surface acoustic wave inthe waveguide structure upon receipt of a suitable RF signal. Thesurface acoustic wave so generated is generally confined between atopmost surface of the waveguide structure and a bottom most surface ofthat same waveguide structure. Depending upon the thickness of thewaveguide structure (device) and the frequency of the RF signal appliedto the transducer, resonant acoustic mode(s) of a relatively thin layer(film) of that waveguide structure proximate to its surface will beexcited and travel along its length. In FIG. 3, such direction isillustrated from right to left.

This traveling, surface acoustic wave will create mechanical strain inthe optical guiding layer and its surrounding material and perturb theguided optical mode such that an induced index perturbation is produced.Such perturbations may be relatively weak—as compared with thosestatically created with lithography—as shown illustratively in FIG.2—but nevertheless sufficient to redirect light out of a device that isonly millimeters long. Advantageously—and according to aspects of thepresent disclosure, the light is emitted in a direction out of planerelative to the planar orientation of the device.

As those skilled in the art will readily appreciate, as the frequency ofthe RF signal is changed, the wavelength of the resonant acoustic modechanges and the period of induced perturbations changes as well. Aspreviously discussed with respect to FIG. 2, since the direction ofemission is dependent on the period of perturbations, changing thefrequency of the RF signal effectively steers emitted light (forexample—in backward and/or forward directions). Note that in FIG. 3,since guided light is traveling toward the acoustic wave in thisillustrative example (right to left in the FIG. 3), the light is blueshifted because of the known Doppler effect. Accordingly, the energy ofthe incoming phonons is added to the energy of the light photonsresulting in higher energy (blue shifted) photons.

Importantly, such a Doppler shift may be useful if emitted light is tobe later mixed with the original light (acting as a local oscillator) tocreate a GHz-scale, beat note away from the baseband and the 1/f noiseof detection devices. If, however, such Doppler shift is not desirablein a particular application, according to the present disclosure theacoustic wave employed may be a standing wave.

FIG. 4 is a schematic illustrating the generation of a standing acousticwave by reflection from a hard boundary that advantageously mayeliminate Doppler shift of emitted light according to aspects of thepresent disclosure. Shown illustratively in that figure, an acoustictransducer—upon receipt of an RF signal—generates a surface acousticwave in an optical waveguide that travels along a length of thatwaveguide. In the direction of travel of that acoustic wave ispositioned a reflective acoustic boundary. The traveling acousticwave—upon striking the reflective acoustic boundary—will reflecttherefrom in a direction back toward the acoustic transducer. Thereflected acoustic wave(s) and the surface acoustic wave(s) meet in aregion in-between the transducer and the reflective boundary and combineto produce a standing surface acoustic wave in that in-between region ofthe waveguide. As previously noted, such a standing surface acousticwave induces perturbations in the waveguide that may effectively directguided light out of that waveguide without exhibiting a Doppler shift.

FIG. 5. is a schematic illustrating the generation of a standingacoustic wave generated by two acoustic transducers that mayadvantageously eliminate Doppler shift of emitted light according toaspects of the present disclosure. As illustratively shown in thatfigure, an optical waveguide structure includes a pair of acoustictransducers positioned a distance apart upon a topmost surface of thatstructure. An RF signal—applied simultaneously to both transducers,generates a surface acoustic wave from each transducer that travelstoward one another in the structure. The traveling waves acousticallyinterfere at a region in-between the two transducers and interfere suchthat a standing surface acoustic wave is produced. The standing surfaceacoustic wave induces perturbations in the waveguide structuresufficient to affect the out-of-plane emission of light guided withinthe waveguide structure (not specifically shown in this figure). Notethat while this FIG. 5 shows only two transducers employed and driven,those skilled in the art will appreciate that alternative numbers and/orarrangements of the transducers are possible and contemplated.

At this point, those skilled in the art will readily understand andappreciate that changing the applied RF frequency may be combined with achange in wavelength of guided light to produce a “rough” and “fine”adjustment of direction of emission.

Note that structures according to the present disclosure mayadvantageously steer light emitted in more than one dimension. Withreference now to FIG. 6, there is shown an illustrative, top-perspectiveview of a schematic waveguide structure employing two acoustictransducers for creating surface acoustic waves in both the longitudinaland lateral directions and steer light out of plane of the structure intwo dimensions. As illustratively shown in that figure, the acoustictransducers are positioned such that emitted surface acoustic wavesemitted from each combine at an angle relative to one another andthereby generate perturbations in the waveguide structure such thatemitted light is steerable over two dimensions by adjusting the RFdriving signal (or the wavelength of the light).

We now note that such sideways light steering may advantageouslyachieved—according to further aspects of the present disclosure—bycreating a phased array. Turning now to FIG. 7, there is shown aschematic illustrating a set of phase shifters implemented in a treestructure and part of a phased array of emitters (antennae) that areconfigured to steer light in a lateral direction while a surfaceacoustic wave steers light in a longitudinal direction—according toaspects of the present disclosure.

As shown in FIG. 7, a phased array antenna structure including a set ofemitters (antenna) are in optical communication with a lightsource—shown in the figure as a laser. Interposed between the emittersand the light source are a set of phase shifters that are illustrativelyarranged in a tree structure. Changes in phase introduced by activatingindividual one(s) of the phase shifters in a prescribed manner cause achange in direction of an emitted phase front of the emitted light. Notethat as shown in this figure the individual phase shifters mayadvantageously be any of a known kind. By adjusting the phase shifters,the emitted light may be steered in a lateral direction. If—according tothe present disclosure—a surface acoustic wave is employed to generate aperturbation in the waveguide emitters, an out of plane coupling isproduced thereby permitting longitudinal steering of the emitted light.

Note that as depicted in FIG. 7, the phased array may be advantageouslyimplemented as a photonic integrated circuit (PIC) on a singlesemiconductor chip—without the laser. When so implemented, the acousticwave as illustrated in that figure will propagate in the entire chip andtherefore will affect all the waveguides comprising the phased arraysimultaneously. When each waveguide has its own individual acoustictransducer however, it is possible to excite one or more individualwaveguides by activating any individual transducer(s) associated withthat/those individual waveguide(s).

FIG. 8 shows a schematic illustrating such a configuration in whichindividual waveguides of a phased array may be excited individually byindividual acoustic transducers according to aspects of the presentdisclosure. As illustrated in that figure, a phased array including aplurality of phase shifters arranged in a tree structure andindividually associated with an emitter, further includes a plurality ofindividual acoustic transducers individually coupled to one of theindividual emitters. Shown further in the figure is that each of theacoustic transducers are individually activated by an individual,respective RF driver signal generated from a common RF source.

Operationally, the phased array receives light emitted from a lasersource coupled to the array. Each one of the individual acoustictransducers specifically excites an acoustic wave into a respectiveoptical waveguide emitter. Advantageously, the phase shifters may adjustthe phase of the optical mode of the light entering an emitter and theacoustic wave(s) generated by the acoustic transducers may furtheraffect the light emission direction. When the RF signal applied to theacoustic transducer(s) is varied the frequency and wavelength of thegenerated acoustic waves are varied and the direction of emission of thelight is varied. Note that the phase shifters employed in theconfiguration illustrated in FIG. 8 may induce an undesirable amount ofloss or consume an undesirable amount of power.

FIG. 9 illustrates an alternative configuration wherein individualacoustic transducers are individually controlled by an individual RFsignal generated by a respective RF generator according to yet anotheraspect of the present disclosure. As may be observed from this figure,there are no phase shifters coupled to the emitters. When so configured,the phase(s) of the RF sources are used to control the phase of theemitted light from each individual one of the optical waveguides(emitters).

Advantageously, and as will be readily appreciated by those skilled inthe art, using the phase of the acoustic wave as the phase controlmechanism in a phased array may eliminate the need for optical phaseshifters. In this method, the sideways direction of emission of theentire array is controlled by the phase of the acoustic waves and thelateral direction of emission is controlled by the frequency of the RFsources. Such a configuration is shown schematically in FIG. 10,illustrating the control of the phases of the acoustic waves to controlthe phased array emission(s)—according to aspects of the presentdisclosure.

Note that the multiple RF sources (shown as one for each acoustictransducer) may be replaced by a common RF generator with adjustabledelays in the signal paths to the acoustic transducers. As the frequencyof all of the RF sources is normally equal (the direction of emissionfrom all emitters is the same), the phased array configurationillustrated in FIG. 9 is simplified to a single, common source and RFdelays that may be tuned by tunable RLC circuits or electrical bufferelements.

At this point we note FIG. 11, which illustrates schematically, andphotomicrographically, structures associated with exciting an acousticmode and guided in an optical (photonic) waveguide. More particularly,show illustratively therein is a schematic diagram of a silicon oninsulator (SOI) structure employing a layered silicon-insulator-siliconsubstrate construction including silicon dioxide insulator and buriedoxide layer (BOX).

As previously noted, to excite acoustic modes within optical waveguides,individual actuators (transducers) positioned on optical waveguides maybe constructed by placing piezoelectric materials on silicon opticalwaveguides. As shown illustratively in FIG. 12, if a patch ofpiezoelectric material is deposited on the top of a silicon waveguideand a voltage is applied between an electrical contact of thepiezoelectric material and the silicon waveguide, an acoustic wave iscreated in the waveguide exhibiting a vertical sheer.

Similarly, and a shown schematically in FIG. 13, if a piezoelectricmaterial is deposited on the side of the optical waveguide and a voltageis applied between an electrical contact of the piezoelectric materialand the silicon optical waveguide the shape of the acoustic wave createdwill exhibit a sideways sheer.

We note at this point that in silicon, the refractive index changesobtainable from compressive waves—in which the density of the materialin some areas is increased and decreased—is higher that the shear wavesin which atoms move in a lateral direction in a crystal structure.

One way of creating a compressive acoustic wave within an opticalwaveguide is achieved placing a piezoelectric transducer at an end ofthe waveguide and illustrated schematically in FIG. 14. The compressiveand expansive force(s) that the piezoelectric material exerts uponactivation produces an expansive and compressive wave that travels down(along) the waveguide and interacts with any guided optical wavetraveling therein.

Another way of creating a compressive wave is achieved by placinginterdigitated piezoelectric materials (transducer forks) on the opticalwaveguide as shown illustratively in FIG. 15. The periodic structure ofthe interdigitated transducer imposes a particular wavelength to theperiod of the created acoustic wave and any perturbation gratingresulting therefrom. Preferably, the length and number of periods of theinterdigitated transducers should be kept relatively small toeffectively excite a wide range of wavelengths.

Yet another way of creating acoustic waves in an optical waveguideaccording to the present disclosure is by directly manipulating theoptical waveguide rather than mechanical excitation via piezoelectrictransducer. Such a method is illustrated schematically in FIG. 16, whichillustrates a periodic series of doped regions within an opticalwaveguide that convert RF electronic energy into an acoustic wave frominternal Coulombic force(s)—according to still another aspect of thepresent disclosure. As may be observed from that FIG. 16, p and n dopedregions are interlaced through an excitation region—which mayadvantageously be undercut for increased efficiency. Of furtheradvantage, side ridge structures may provide for electrical contacts tothe doped regions while an emission portion of the waveguide does notrequire electrical contact(s) or ridge structure(s).

Electrooptic Tuning

Another approach for dynamically tuning emission direction(s) accordingto the present disclosure employs static lithographically gratings andchange its effective period by modifying its effective index. Asillustrated previously in FIG. 2, the direction of emission isdetermined by the wave vector of the grating namely,

$K = {\eta_{eff}{\frac{2\; \pi}{\Lambda}.}}$

Note that if the period of the grating, A, is fixed, its wave vector Kmay be tuned by modifying the effective index η_(neff). As shownillustratively in FIG. 17, when the effective index of a guidingstructure is changed, the phase matching condition

${K_{x} = {\frac{2\; \pi}{\lambda} - {\eta_{eff}\frac{2\; \pi}{\Lambda}}}},$

in which K_(x) is the horizontal component of the radiation wave vectorwhich—when changed—changes the angle of emission. In particular thelarger the effective index of the waveguide becomes, the more backwardthe direction of emission.

Advantageously, there are several methods according to the presentdisclosure for modifying the effective index of the guided mode. Localheating of the waveguide can decrease the effective index, fluidicintegration can modify the index of regions surrounding the waveguide,and electrooptic effects can modulate the index of a waveguide gratingdirectly. Note that if the number of gratings is large—as in a largephased array—the power consumed of the whole aperture becomes animportant consideration and electrooptic effect mechanisms is anattractive option in such configurations. In material and structuresexhibiting a second order susceptibilities, Pockels (linearelectro-optic effect) in which the refractive index change isproportional to the electric field may be employed to modify therefractive index with an electric field. In silicon waveguides, either afree carrier effect or DC Kerr effect (quadratic electro-optic effect)can be advantageously employed to locally modify the refractive index.When free carriers are injected or depleted from a semiconductor lightguiding material such as a silicon waveguide, a plasma dispersion effectalters the refractive index of the material.

For example, FIG. 18 illustratively shows in schematic form that biasinga pn junction across a silicon waveguide can change its refractive indexand result in steering of a light beam due to a change in the effectiveperiod of a grating structure (Λ_(eff)=Λ/η_(neff)). More particularly,the application of a voltage across the pn junction changes the freecarrier density in the waveguide and effectively tunes the direction ofemission. Accordingly, the structure illustratively shown in FIG. 18 maybe used to fine tune the direction of emission. However, since theelectrooptic effect due to free carriers is a relatively small effect,the effective period of the grating is changed only slightly around theperiod set by periodic perturbation structures. As a result, structuressuch as that shown in FIG. 18 will not generally steer light across anentire field of view.

Alternatively—and according to still another aspect of the presentdisclosure—free carriers themselves may be the perturbation mechanismand advantageously achieve full tunability of a grating structure. Withreference to FIG. 19, there is shown an illustrative schematic of avoltage controlled pn junction acting as a tunable junction. Note thatthe width of the intrinsic region and any charge accumulation in thedoped regions is a function of the local voltage. If the voltage acrossthe pn junction is a periodic function of the position along thewaveguide, the refractive index change created by the free carrierplasma effect is periodic and therefore such structures will emit lightin the direction that satisfies the phase matching condition.

To create the above-noted periodic voltage distribution along thewaveguide, doping regions may be segmented into small section eachcontrolled by an individual voltage and separated by neighboringsections by an intrinsic region as illustrative shown schematically inFIG. 20. As illustrated in that figure, and according to yet anotheraspect of the present disclosure, by applying a periodic voltage to pnjunction segments the refractive index of the guiding structure isperturbed.

Advantageously, each section may be individually controlled by anindividual voltage and essentially any desirable perturbation may becreated across the waveguides. Since gratings created in this manner areinherently weak due—in part—to the small perturbation induced by thefree carrier, the length of the grating should preferably be thousandsof periods long. Of course, such “long” gratings require thousands ofindividual voltage controls.

Advantageously, if a photonics structure such as that illustrated in thefigure is directly controlled by a CMOS driving circuit, individualdriving transistors may be programmed to drive the photonics gratingwith a desired voltage pattern. If, on the other hand, the number ofrequired control (driving) signals/connections is not available, astanding wave RF signal may be maintained along any electrodes feedingthe pn junctions. Such standing wave function, having a period with isdependent upon the frequency of an applied RF signal, may be sampledwith discrete contacts along the length of a pn junction waveguide tocreate the desired periodic charge accumulation pattern along thewaveguide.

Turning now to FIG. 21, there is shown a schematic illustrating astanding wave RF signal creating a periodic pattern required for agrating wherein the period of the grating is tuned with the frequency ofthe RF signal—according to aspects of the present disclosure. Note thatone challenge in creating devices having a pn junction gratingperturbation mechanism is that fabrication of sub-wavelength segmentsrequired can be difficult due to the straggle dopants experience whilebeing implanted into the waveguide.

An alternative method to these pn junction devices are devices employingcapacitive induction of free carrier accumulation regions. For example,as illustratively shown in FIG. 22, a voltage applied to a semiconductorpositioned on top (or other location) of a light conducting waveguidecan induce accumulation of free carriers in a small portion of thewaveguide and locally perturb its effective index. As illustrativelyshown in that figure, application of a voltage to thesemiconductor-on-semiconductor capacitor leads to a charge build up inthe region. Similar to that illustratively shown in FIG. 20, if thelength of waveguide is divided into a large number of smallsegments—each individually controlled by a different voltage along thelength of the waveguide—a periodic pattern of carrier inducedperturbation can be created along the length of the waveguide which inturn acts as a tunable grating. FIG. 23 illustratively shows theapplication of a periodic pattern of voltages to polysilicon segmentsresults in a periodic index perturbation in a silicon waveguide.

As may be observed from FIG. 23, small sections (pieces) of polysiliconsemiconductor can be deposited on top of a silicon waveguide. A thin(few nanometers) layer of an insulating material such as silicon dioxidemay be sandwiched between the silicon waveguide and the polysiliconsegments. Both the silicon waveguide and the polysilicon segments shouldbe slightly doped to conduct carriers sufficiently. The doping of bothhowever should be slight enough to reduce loss the optical modeexperiences as it travels along the silicon waveguide. The opticalmode—in a preferred embodiment—should be tightly confined to the siliconwaveguides so that it should not interact with the thin and smallpolysilicon segments as if they were part of a static perturbinggrating.

FIG. 24 is a schematic illustrating short and thin segments ofpolysilicon deposited above a silicon waveguide controlled by individualvoltages according to aspects of the present disclosure. As may beobserved from that figure, a large number of segments of polysilicon aredeposited or otherwise positioned on top of the silicon opticalwaveguide. The segment length (L) and the gap between the segments issufficiently small such that several of these will fit within onedesired period length. If the number of segments in one period is not alarge number, the periodic voltage function may be down-sampled and thiswill lead to loss to unwanted radiation modes. Notwithstanding, if thevoltage to all electrodes is independently controlled, a wavelengthsweep can be continuous without the need for the wavelength to be aninteger multiple of the segments' period. Advantageously, in mostcircumstances, all of the waveguide members of a phased array have thesame grating pattern, so the voltage used to create the grating may beapplied to all waveguides simultaneously. In fact, the same polysiliconsegment may be extended over the entire array to charge up and perturball waveguides at the same time. FIG. 25 is a schematic illustratinglong segments of polysilicon used to excite all waveguides in parallelas part of a phased array according to aspects of the presentdisclosure.

Note that as discussed previously with respect to the pn junction-basedstructures, the thousands of individual voltages required to create atunable periodic voltage pattern might not be available if direct CMOScontrol of a grating is not implemented. Similar to the pnjunction-based structures, an RF standing wave may be imposed on ametallic wire running parallel to the waveguide such that a desiredperiodic voltage pattern is induced onto the waveguide. As may beobserved in illustrative FIG. 26 there is shown a standing RF signalinducing periodic voltage patterns in an optical waveguide according toaspects of the present disclosure. The segments shown therein—which areillustratively formed from polysilicon—“sample” the periodic voltagefunction at regular intervals and induce a periodic charge accumulationpattern along the length of the waveguide. Advantageously, by changingthe frequency of the RF standing wave the period of the induced gratingand the direction of emission may be tuned as desired. The highfrequency of the RF wave to achieve this required period for emissionout of a silicon waveguide might be undesirable.

At this point, while we have presented this disclosure using somespecific examples, those skilled in the art will recognize that ourteachings are not so limited. Accordingly, this disclosure should beonly limited by the scope of the claims attached hereto.

1. A method of forming an optical structure comprising: providing anoptical waveguide having a light guiding core; inducing dynamic indexperturbations into the optical waveguide, said dynamic indexperturbations sufficient to affect the emission of light traversing theoptical waveguide, said emission in a direction out-of-plane relative tothe waveguide.
 2. The method of claim 1 wherein said dynamic indexperturbations are induced through the effect of an acoustic transducer.3. The method of claim 1 wherein the dynamic index perturbations areinduced through an electro-optic effect.
 4. The method of claim 2wherein the acoustic transducer is driven at a frequency of at least 1GHz.
 5. The method of claim 1 wherein said dynamic index perturbationsare induced through the effect of one or more thermo-optic phaseshifter(s).
 6. The method of claim 1 wherein the dynamic indexperturbations are induced through the effect of a plurality of acoustictransducers.
 7. The method of claim 6 wherein the plurality of acoustictransducers are configured such that acoustic waves generated therefromtravel along a common axis.
 8. The method of claim 6 wherein theplurality of acoustic transducers are configured such that acousticwaves generated therefrom travel along at least one non-common axis. 9.The method of claim 1 further comprising varying the induced dynamicindex perturbations over time.
 10. The method of claim 1 wherein thecore of the optical waveguide exhibits a thickness of less than 1λ,where λ is the wavelength of the light traversing the optical waveguide.11. The method of claim 2 wherein the acoustic transducer is in physicalcontact with the core of the optical waveguide.
 12. The method of claim1 wherein at least a portion of the out-of-plane emission of the lightis in a perpendicular direction relative to a direction of travel of thetraversing light.
 13. The method of claim 1 wherein said dynamic indexperturbations are varied such that an emission angle associated with theout-of-plane emission varies with the varying dynamic indexperturbations.
 14. The method of claim 6 wherein the plurality ofacoustic transducers are interdigitally arranged.
 16. The method ofclaim 6 wherein the plurality of acoustic transducers includes twoacoustic reflectors positioned opposite one another in the opticalwaveguide such that an acoustic cavity is formed therein.
 16. The methodof claim 6 wherein each individual one of the plurality of acoustictransducers is formed from one or more pn junctions.
 17. The method ofclaim 5 wherein the electro-optic effector includes a plurality ofinterdigitally arranged individual effectors.
 18. The method of claim 14wherein the plurality of interdigitally arranged transducers areoperationally activated with a phase offset relative to any adjacenttransducer.
 19. The method of claim 18 wherein the phase offset, θ,relative to any adjacent transducer is given by θ_(i)=θ_(i-1)+Δθ tosteer the out of plane beam, where i is the antenna number and phasechange between adjacent antennas are given by Δθ, 0<Δθ<2π.
 20. Themethod of claim 14, wherein the plurality of interdigitally arrangedtransducers are piezoelectric.
 21. The method of claim 1, wherein theoptical structure is part of a phased array.
 22. The method of claim 21,wherein the phased array includes a plurality of emitters, eachindividual one of the emitters including an individual one of theoptical structure.
 23. The method of claim 22, wherein each individualone of the optical structures includes an acoustic transducer that uponactivation induces the dynamic index perturbations into the waveguide,the acoustic transducers operationally driven by an RF signaloriginating from a common source.
 24. The method of claim 22, whereineach individual one of the optical structures includes an acoustictransducer that upon activation induces the dynamic index perturbationsinto the waveguide, the acoustic transducers operationally driven by anindividual RF signal originating from a respective individual source,each individual RF signal exhibiting a different frequency from theother individual RF signals.
 25. The method of claim 19, wherein eachindividual one of the optical structures includes an acoustic transducerthat upon activation induces the dynamic index perturbations into thewaveguide, the acoustic transducers operationally driven by anindividual RF signal originating from a respective individual source,each individual RF signal exhibiting a different phase offset from theother individual RF signals.
 26. An optical device comprising: anoptical waveguide including a light guiding section; a dynamic indexperturbation generator configured to dynamically generate indexperturbations in the light guiding section; such that upon activation ofthe dynamic index perturbation generator and the generation of indexperturbations in the light guiding section, light traversing the lightguiding section is emitted in a direction out-of-plane relative to thelight guiding section.
 27. The optical device of claim 26 wherein thedynamic index perturbation generator includes an acoustic transducer.28. The optical device of claim 26 wherein the dynamic indexperturbations are induced by an electro-optic effector.
 29. The opticaldevice of claim 27 wherein the dynamic index perturbation generator isdriven at a frequency of at least 1 GHz.
 30. The optical device of claim26 wherein the dynamic index perturbations are induced by a thermo-opticeffector.
 31. The optical device of claim 27 wherein the dynamic indexperturbation generator includes a plurality of acoustic transducers. 32.The optical device of claim 31 wherein the plurality of acoustictransducers are configured to generate acoustic waves that travel alonga common axis.
 33. The optical device of claim 31 wherein the pluralityof acoustic transducers are configured to generate acoustic waves thattravel along at least one non-common axis.
 34. The optical device ofclaim 26 wherein the dynamic index perturbation generator is configuredto vary the induced dynamic index perturbations over time.
 35. Theoptical device of claim 26 wherein the light guiding section exhibits athickness of less than 1λ, where λ, is the wavelength of the lighttraversing the optical waveguide.
 36. The optical device of claim ofclaim 27 wherein the acoustic transducer is in physical contact with thelight guiding section.
 37. The optical device of claim 26 configuredsuch that at least a portion of the out-of-plane emission of the lightis in a perpendicular direction relative to a direction of travel of thetraversing light.
 38. The optical device of claim 26 wherein the dynamicindex perturbation generator is configured such that the dynamic indexperturbations are varied and an emission angle associated with theout-of-plane emission varies with the varying dynamic indexperturbations.
 39. The optical device of claim 31 wherein the pluralityof acoustic transducers are interdigitally arranged.
 40. The opticaldevice of claim 31 wherein the plurality of acoustic transducersincludes two acoustic reflectors positioned opposite one another in theoptical waveguide such that an acoustic cavity is formed therein. 41.The optical device of claim 31 wherein each individual one of theplurality of acoustic transducers is formed from one or morepn-junctions.
 42. The optical device of claim 28 wherein theelectro-optic effector includes a plurality of interdigitally arrangedindividual effectors.
 43. The optical device of claim 42 wherein theplurality of interdigitally arranged transducers are operationallyactivated with a phase offset relative to any adjacent transducer. 44.The optical device of claim 42, wherein the plurality of interdigitallyarranged transducers are piezoelectric.
 45. The optical device of claim44 wherein the plurality of interdigitally arranged transducers areoperationally activated with a phase offset relative to any adjacenttransducer.
 46. The optical device of claim 44, wherein each individualone of the optical structures includes an acoustic transducer that uponactivation induces the dynamic index perturbations into the waveguide,the acoustic transducers operationally driven by an RF signaloriginating from a common source.
 47. The method of claim 44, whereineach individual one of the optical structures includes an acoustictransducer that upon activation induces the dynamic index perturbationsinto the waveguide, the acoustic transducers operationally driven by anindividual RF signal originating from a respective individual source,each individual RF signal exhibiting a different frequency from theother individual RF signals.
 48. The method of claim 44, wherein eachindividual one of the optical structures includes an acoustic transducerthat upon activation induces the dynamic index perturbations into thewaveguide, the acoustic transducers operationally driven by anindividual RF signal originating from a respective individual source,each individual RF signal exhibiting a different phase offset from theother individual RF signals.
 49. An optical phased array comprising: aplurality of emitters, each individual emitter including; an opticalwaveguide including a light guiding section; a dynamic indexperturbation generator configured to dynamically generate indexperturbations in the light guiding section.
 50. The optical phased arrayof claim 49 configured such that upon activation of the dynamic indexperturbation generator and the generation of index perturbations in thelight guiding section, light traversing the light guiding section isemitted in a direction out-of-plane relative to the light guidingsection.
 51. The optical device of claim 49 wherein the dynamic indexperturbation generator includes an acoustic transducer.
 52. The opticaldevice of claim 49 wherein the dynamic index perturbations are inducedby an electro-optic effector.
 53. The optical device of claim 49 whereinthe dynamic index perturbation generator is driven at a frequency of atleast 1 GHz.
 54. The optical device of claim 49 wherein the dynamicindex perturbation generator includes a plurality of acoustictransducers.